1. Field of the Invention
This invention relates to a direct current transformer, and particularly to a transformer in which the secondary winding is made of a magnetoresistive material.
2. General Description of the Prior Art
The D.C. transformer was invented by Giaever in 1965, and in its simplest form, consists of closely spaced, but insulated, thin films of superconductive material, one constituting a primary and the other the secondary of the transformer. Typically, the windings are magnetically biased by an auxiliary magnet or electromagnet and the assembly placed in liquid helium to lower the temperature to approximately 4.degree. K. (-269.degree. C.), and thus to produce superconductivity in the transformer windings and in the electromagnet. Superconductive materials are diamagnetic, and thus initially the magnetic field does not penetrate the windings. However, when the flux level present is raised above a critical value, magnetic vortices pass through the primary. Then, by virtue of the application of current to the primary winding, the magnetic vortices are caused to be moved at right angles to the current flow, and thus there is created a moving magnetic field. Alternatively in the absence of an auxiliary magnet, the vortices result from the primary current itself. The moving magnetic field is coupled to the secondary by virtue of its close proximity, and it thereby produces an output potential across the secondary which is a function of the applied current.
There are several disadvantages with existing D.C. transformers, and these may be summarized as follows:
1. The vortices in the secondary area experience a pinning force which opposes flux motion in the secondary. As a result, transformer action is restricted to rather high values of current and applied magnetic fields. At low currents and fields, the flux motion of the primary is not as effective in causing flux motion in the secondary.
2. The superconductive type transformer will not work at temperatures higher than the transition temperature of the secondary.
It is an object of this invention to overcome the aforesaid difficulties and to generally provide an improved D.C. transformer.
It is a specific object of this invention to provide a D.C. transformer in which the magnetic flux flow in the primary will result in a space modulated flux motion in a magnetoresistive secondary.
A still further object of this invention is to provide a D.C. transformer in which there is a net flux flow voltage across both the primary and secondary due to space modulated flux motion across them.